1. Field of the Invention
The present invention relates to methods and compositions for grouting heat exchange pipe, and more particularly, to grouting such pipe in holes or trenches.
2. Description of the Prior Art
Ground source heat pumps have been utilized heretofore for providing residential and commercial space heating and cooling. A ground source heat pump is similar to conventional air conditioners and heat pumps except that it utilizes the ground to dissipate or collect heat instead of atmospheric air. Since ground temperatures are generally close to residential and commercial room temperatures, ground source heat pumps are cost-effective alternatives to conventional systems in many locations. The cost-effectiveness of ground source heat pumps depends on the climate in the area in which such heat pumps are to be installed, the thermal properties of the ground at that location, the cost of energy at the location and the effectiveness of the heat exchanger utilized to transfer heat to or from the heat pump. The outside heat exchanger connected to a ground source heat pump is usually a loop of plastic pipe which is placed in a hole or trench and sealed therein with a grouting composition. A liquid such as water with or without antifreeze is circulated through the heat exchange pipe loop whereby it collects heat from the ground during the winter or transfers heat into the ground during the summer to thereby heat or cool residential or commercial space. In addition, ground source heat pumps can optionally include heat exchange apparatus to provide free hot water in the summer and substantial hot water savings in the winter.
As mentioned, the ground source heat pump heat exchange pipe loop can be installed in a trench parallel to the ground surface or in a substantially vertical deep hole formed in the ground. The particular configuration utilized depends on the area of the available ground as well as the make-up of the ground, e.g., the quantity of rock contained therein, etc.
Grouting the heat exchange pipe loop, particularly in installations of the pipe in vertical deep holes, is an extremely important aspect of ground source heat pump efficiency and performance. The grouting composition sets into a substantially impermeable mass which functions to position the pipe in the hole and to seal the surfaces of the pipe to the ground. The seal between the pipe and the ground insures that the proper heat transfer between the pipe and the ground takes place. If the grouting composition is not placed completely around and along the entire length of the pipe, the heat transfer will be seriously reduced. In addition, the grouting composition must have high heat transfer properties so that heat will readily and efficiently transfer between the fluid inside the pipe loop and the ground by way of the grouting composition. The grouting of the heat transfer pipe accomplishes a number of environmental protection requirements as follows. The set grout and seal provided thereby protects water reservoirs penetrated by the hole, i.e., the set grout prevents leakage from the surface into water reservoirs by way of the hole penetrating the reservoirs thereby preventing contamination of the reservoirs. The presence of the set grout also prevents flow between formations penetrated by the hole, e.g., between salt water and fresh water containing formations. The set grout also seals formations or zones containing pressurized fluid thereby preventing blow-outs through the hole to the surface.
In order to accomplish the various objectives mentioned above, the grouting composition used should have the following properties. The grouting composition must have a high thermal conductivity upon setting to provide the required heat transfer between the heat exchange pipe and the walls of the hole in the ground. The grouting composition must have a low viscosity during placement so that it can enter the space between the walls of the pipe loop and the hole in the ground without leaving voids containing air that reduce heat transfer. In addition, the grouting composition must not shrink during setting so that voids or channels are not formed which reduce heat transfer between the heat exchange pipe and the ground and/or allow pressurized fluids to flow between formations or to the surface.
While compositions for grouting heat pump heat exchange pipes in the ground have been developed and used heretofore, there is a continuing need for an improved grouting composition which has the properties set forth above.
The present invention provides methods and compositions for grouting heat exchange pipe which meet the needs described above and overcome the deficiencies of the prior art. The grouting compositions of this invention quickly set and have high thermal conductivities. The grouting compositions are basically comprised of an amorphous silica material selected from the group consisting of fly ash, condensed silica fume, rice hull ash, natural pozzolan and mixtures of two or more of such materials; a water swellable clay selected from the group consisting of Wyoming sodium bentonite and Western sodium bentonite; water present in an amount sufficient to form a slurry; and an alkaline earth metal oxide or hydroxide present in an amount sufficient to react with the amorphous silica material in the presence of water to form a cementitious composition which sets into a hard substantially impermeable mass. The grouting composition optionally also includes a set retarding agent and a thermal conductivity increasing agent.
A particularly preferred grouting composition of this invention having the above mentioned properties is comprised of ASTM Class C fly ash, condensed silica furne, sodium bentonite, a citric acid set retarder, a thermal conductivity increasing agent comprised of desulfurized coke containing at least 80% by weight carbon and fresh water present in an amount sufficient to form a slurry.
The methods of this invention for grouting a heat exchange pipe in a hole or trench in the ground are comprised of the following steps. A quick set low permeability grouting composition having high thermal conductivity is prepared comprised of an amorphous silica material, a water swellable clay, an alkaline earth metal oxide or hydroxide and water. The grouting composition is placed in the hole or trench between the ground and the walls of the pipe, and the grouting composition is allowed to set therein.
It is, therefore, a general object of the present invention to provide improved methods and compositions for grouting heat exchange pipes.
Other and further objects, features and advantages of the present invention will be readily apparent to those skilled in the art upon a reading of the description of preferred embodiments which follows.